The present invention relates to short pulse laser system, and more particularly, to a method for determining a minimum pulse width for a pulsed laser beam in a short pulse laser system.
Ultrafast lasers generate intense laser pulses with durations from roughly 10-11 seconds (10 picoseconds) to 10-14 seconds (10 femtoseconds). A wide variety of potential applications for ultrafast lasers in medicine, chemistry, and communications are being developed and implemented. These lasers are also a useful tool for milling or drilling holes in a wide range of materials. Hole sizes as small as a few microns, even sub-microns, can readily be drilled. High aspect ratio holes can be drilled in hard materials, such as cooling channels in turbine blades, nozzles in ink-jet printers, or via holes in printed circuit boards.
Laser drilling of holes in a particular pattern using optical parallel processing has been used for a variety of fast and ultrafast laser applications, and is generally applied using projection imaging of a mask containing the pattern (usually at a magnification), or a beamsplitter, such as a diffractive optical element (diffractive optical element). Optical parallel processing is desirable in order to enable mass production techniques to increase throughput and quickly create customer-specified geometries in final products. These geometries often require multiple small holes to be drilled in a particular pattern that must be accurate, consistent, and repeatable from workpiece (the material the laser is drilling) to workpiece.
Parallel processing using a beam splitter usually has the advantage over mask projection imaging that it has high light utilization efficiency, hence higher drilling speed. However, there are special challenges to using a diffractive optical element in ultrashort laser processing applications. Ultrashort laser pulses have much larger spectral bandwidth compared long pulses, i.e., they contain many wavelength components, and the diffractive optical element is spectrally dispersive, i.e. different wavelengths are diffracted in different directions. It is necessary to understand the behavior and limitations of using a diffractive optical element in ultrashort laser processing in order to select the correct laser for the parallel processing system.
Consequently, in a market that measures its annual revenue in millions of dollars, the company that develops new methods of making laser micromachining tools more accurate and efficient will help to optimize performance and minimize production cost in a wide variety of applications within the laser micromachining industry.
In accordance with the present invention, a method is provided for determining a minimum pulse width for a pulsed laser beam in a short pulse laser system, such that the minimum pulse width accounts for dispersion associated with the pulse laser beam passing through a diffractive optical element. The method includes: determining size data for an ablation to be formed in a surface of a workpiece; determining an operating wavelength for a pulsed laser beam; determining spot size data for the beam incident on the workpiece; determining tolerance data for the spot size of the incident beam; and determining a minimum pulse width for the pulsed laser beam based on the size data for the ablation, the operating wavelength for the laser beam, the spot size data for the laser beam and the tolerance data for the spot size.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.